FIG. 4 is a cross sectional view of a conventional loudspeaker 501 disclosed in patent document 1. A voice coil 502A is located movably near a magnetic circuit 501A, and is joined to an inner rim of a diaphragm 503A. An outer rim of the diaphragm 503A is joined to an edge 504A joined to a frame 505A. A back side of the diaphragm 503A is joined to a suspension holder 506A. The suspension holder 506A is joined to edge 507A joined to the frame 505A. The edges 504A and 507A protrude in opposite directions so that the vertically vibrating excursion of the diaphragm 503A is equal in both upward and downward directions, hence suppressing distortion of the loudspeaker 501.
The suspension holder 506A is joined to the back side of the diaphragm 503a, hence vibrating together with the diaphragm 503A. A vibrating portion including the suspension holder 506A and the diaphragm 503A has a significantly large weight. This weight is not a big issue when the loudspeaker 501 reproducing lower-frequency sound. However, the weight may decline the driving efficiency of the loudspeaker 501 during the reproduction of medium-frequency or higher-frequency sound.
Patent Document 1: JP2004-7332A